The present invention relates to knitted therapeutic medical compression garments. More particularly, the present invention relates to knit therapeutic graduated compression stockings having courses of crimped bi-component yarns having an elastomeric core with a thermoplastic sheath and inlay courses containing spandex yarn.
Therapeutic medical compression stockings have been used on a relatively wide scale to assist in the prevention of venous diseases and/or embolism in a patient. The purpose of such stockings is to overcome the elevated internal pressures within a human extremity caused by gravity or disease processes.
The pressure gradient stocking and its use are well documented in the literature. The custom pressure gradient stocking was developed by Conrad Jobst a sufferer of venous disease. Mr. Jobst found relief from his problem while standing in a swimming pool. Mr. Jobst reasoned that the water pressure in the pool, which increases with depth, cancelled out the internal pressure in the veins of his leg. Jobst and others have identified a need to apply a relatively large compressive force in proximity to the ankle. See, page 535 of the article entitled xe2x80x9cConrad Jobst and the Development of Pressure Gradient Therapy for Venous Disease.xe2x80x9d Also see, the article entitled xe2x80x9cTreatment of venous diseasexe2x80x94The innovatorsxe2x80x9d at page 681 thereof quoting from an article by J. Horner, et al. entitled xe2x80x9cValue of graduated compression stockings in deep venous insufficiency,xe2x80x9d Br Med J. 1980; zz: 820-1 wherein it is stated xe2x80x9cthe greater the compression gradient between the ankle and calf produced by the stocking, the lower the ambulatory pressures.xe2x80x9d Cited in U.S. Pat. No. 5,823,195.
Therapeutic medical graduated compression stockings are designed to provide sufficient external circumferential counter pressure to maintain the normal venous and lymphatic pressures at a given level in the extremity, thus assisting the movement of venous blood and lymph from the extremity. Another important effect of compression is the reduction of the venous volume. Reduction of venous volume leads to an increase of the venous flow velocity. Gerwen H J L van. Pressure gradient tolerance in compression hosiery. Katholike Universiteit Nijmegen. 1994, pp. 103-105.
Furthermore, while the exact mechanism(s) of action of gradient compression therapy remain unknown improvements in skin and subcutaneous tissue microcirculatory hemodynamics may contribute to the benefits of compression therapy. The direct effect of compression on subcutaneous pressure is a plausible mechanism. Edema reduction and edema prevention is the goal in patients with chronic venous insufficiency, lymphedema, and other edema causing conditions. Subcutaneous pressures increase with elastic compression. Nehler M R, Moneta G L, Woodard D M, et al. Perimalleolar subcutaneous pressure effects of elastic compression stockings. J Vasc Surg 1993;18(5):783-88. This rise in subcutaneous tissue pressure should act to counter transcapillary Starling forces, which favor leakage of fluid out of the capillary.
For instance, gradient compression stockings 20 mmHg and above have demonstrated the following effects in persons with venous insufficiency:
Improved venous hemodynamics
Prolonged (more normalized) venous refill time (VRT). Samson R H, Scher L A, Veith F J, et al. Compression stocking therapy for patients with chronic venous insufficiency. J Cardiovasc Surg 1985;26:10.
Reduced venous volume and increased venous flow velocity Reduction and control of edema. Dale W A. The Swollen Limb in Current Problems In Surgery, edited by Mark M Ravitch, et al. 1973 Year Book Medical Pub, Chicago. p. 29-31.
Most of the patients suffering from minor to moderate varicosities, moderate edema, superficial thronbophlebitis, and post sclerotherapy need to use stockings with the compression at ankle in the range from 15-20 to 20-30 mm Hg. More complicated and severe cases require pressure of 40 mm Hg and higher.
A variety of therapeutic medical graduated compression stockings are on the market today. The stockings of various descriptions have been proposed. Unfortunately, therapeutic stockings, in order to provide the necessary compression, are often thick and rather unsightly or have other drawbacks. An example of a therapeutic stocking is described in U.S. Pat. No. 3,975,929 which describes a thigh length anti-embolism stocking made with alternating courses of covered spandex yarn on a circular hosiery knitting machine. Another example of a therapeutic stocking is described in U.S. Pat. No. 4,069,515 to Swallow, et al., which discloses a non-slip therapeutic stocking having a covered elastomeric yarn (spandex core-nylon covering) inlaid into every other course of the jersey knit stitches made of stretch nylon. In particular, the Swallow patent describes the foot portion as having alternating courses of jersey knit stitches of non-elastomeric yarn. One of these yarns is a Z-twist stretch nylon and the other is an S-twist nylon. A covered elastomeric yarn such as a single covered elastomeric yarn having a 280 denier spandex core and covered with nylon 6 yarn is preferably inlaid into every other course of the jersey stitches.
The use of bi-component crimped yarns is known in the manufacture of pantyhose. Such garment construction is described in U.S. Pat. No. 5,352,518 to Muramoto, et al., who teach a stocking having a bi-component core and sheath type yarn wherein the sheath is composed of a fiber forming a thermoplastic polymer and the core is composed of a fiber forming elastomer. It is stated that the filament has excellent elastic properties, a small surface friction coefficient and a matting effect due to diffusion reflection of light caused by rough surfaces, and is agreeable when worn in the form of a knitted textile structure, particularly as a lady""s stocking.
A principle feature of the present invention is the provision of a therapeutic medical compression stocking made with bi-component fibers. It has been found that the use of bi-component yarns, in particular, those crimped yarns having an elastomeric core and a thermoplastic sheath when knit with inlaid courses of spandex or spandex covered with a bi-component yarn form therapeutic stockings that provide excellent compression control. In addition, these therapeutic stockings are more transparent than conventional therapeutic stockings. The therapeutic stockings of the present invention may be knit on a conventional circular knitting machine.
In a first preferred embodiment every course of the therapeutic stocking is knit with a crimped bi-component yarn having an elastomeric core and a thermoplastic sheath. Courses of an inlay yarn of spandex are provided at least every third course. In a second embodiment, the therapeutic stocking is knit with every other course being the crimped bi-component yarn and the inlay yarn is spandex present in every course. The alternate courses are covered spandex yarn. It was found that the use of spandex yarns in combination with the bi-component yarn enables the reduction in size of the spandex used in the inlay courses and maintains the desired compression.
In yet another embodiment of the present invention, there is provided a knitted therapeutic stocking comprising a crimped bi-component yarn in every course and an inlay yarn of spandex covered with a bi-component yarn. In a fourth embodiment there is provided a knitted therapeutic stocking comprising a crimped bi-component yarn in every other course and inlay course of spandex covered with a bi-component yarn.
It has been found that the therapeutic medical compression stockings of this invention provide a smooth, silky, cool and supple hand of fabric; easier donning, lighter weight, good durability and very good compliance with patient needs.
It is an object of the present invention to provide a therapeutic stocking having excellent compression by using an improved bi-component crimped yarn of the present invention.
Another object of the present invention is to provide an improved air-permeable therapeutic stocking because the spandex inlay yarns do not need to be covered.
Yet another object of the present invention is to provide a therapeutic stocking having improved transparency.